A wooden gate is a heavy rectangle hanging off one edge, and gravity works on it every single swing. The hinge side carries the load while the latch side slowly drops, until one day the latch misses its catch and you're lifting the gate by the handle just to close it. Wood swelling and shrinking with the seasons speeds the whole process up.
Three different parts can cause the same droop, and each one has a different fix: loose hinges, a frame that has racked into a parallelogram, or a post that leans. Guessing wrong means fixing a part that was never broken. So diagnose first, then spend money.
Measure the diagonals. Run the tape from the top hinge-side corner down to the bottom latch-side corner, then measure the other diagonal. Equal numbers mean the frame is still square, and your problem is hinges or post. Numbers that differ by half an inch or more mean the frame itself has racked, and it needs bracing or a cable.
Check the post. Put the level against the hinge post in both directions. A post leaning even an inch at the top drags the whole gate down with it, and no amount of frame work compensates. Push the post hard with your shoulder. If it rocks in its hole, that's your answer.
Wiggle the gate. Lift the latch side gently and watch the hinges. Movement at the hinge screws — the gate shifting before the frame does — points to screws that have wallowed out their holes in weather-softened wood.
Replace the hinge screws with longer ones. Pull one screw from the top hinge and look at it. Gate hinges often go up with screws barely an inch long that bite only into the gate frame, not the post behind it. Swap them, one at a time so the gate never hangs loose, for 3-inch exterior screws that reach solid post wood. This single step fixes a surprising share of sagging gates. It's the same long-screw cure that works on a door hinge that squeaks and sags indoors.
Straighten or upgrade the hinges. A bent hinge leaf never holds a gate level again. If a leaf is visibly twisted, replace the hinge with a heavier one rated for the gate's weight. Wide gates on two small hinges also benefit from a third hinge in the middle, which spreads the load the top hinge was carrying alone.
Square the frame with a cable kit or a brace. An anti-sag kit runs a cable from the top corner on the hinge side down to the bottom corner on the latch side, with a turnbuckle in the middle. Tighten the turnbuckle a little at a time, checking the latch as you go, until the gate hangs level and the diagonals match again. Prefer wood? A solid diagonal brace works the opposite way, in compression: it runs from the bottom corner on the hinge side up to the top corner on the latch side. Mixing up the two directions is the classic mistake — a cable on the brace's diagonal just goes slack and does nothing.
Add a gate wheel on wide gates. Once a gate gets past about five feet wide, or it's built from heavy lumber, a spring-loaded caster under the latch-side corner carries the weight the hinges were never meant to hold alone. Mount it so the wheel touches the ground with the gate closed. This is an add-on, not a substitute — square the frame first, then let the wheel keep it that way.
Fix a leaning post at the post. If the post rocks but the wood is sound, dig down beside it, push it plumb, and pour fresh concrete around the base. A post rotted through at ground level has to be replaced; bracing a gate against a dying post just buys a season. This is the only fix on the list that's a half-day job instead of an hour, and it's the one people most often skip straight past. When the lean runs down the fence line instead of stopping at the gate post, the same dig-out, plumb, and reset approach applies to the line posts too — our guide to fixing a leaning fence walks through the full repair.
Installing the brace backwards. Cable high-to-low on the latch diagonal, wood low-to-high. Get it reversed and you've added hardware that does nothing at all, which is worse than doing nothing, because now you think the gate is braced.
Cranking the turnbuckle until the gate lifts. The goal is a square frame, not a raised one. Overtightening bows the gate the opposite direction and makes it bind against the latch post at the top.
Rebuilding the gate when the post leans. A perfect gate on a post that's an inch out of plumb still sags by exactly that inch. Level check first, every time.
Work the order: screws, hinges, frame, post. Most sagging gates are a $5 pack of long screws or a $15 cable kit away from latching cleanly again, and the whole diagnosis takes two minutes with a tape measure. Add the hinge check to your yearly summer home maintenance walk-around and you'll usually catch the droop at the screwdriver stage, not the rebuild stage.
Because the causes don't stop: wood absorbs moisture and gets heavier, screws slowly work in softened holes, and the frame racks a little with every season of swinging. A cable kit or proper diagonal brace holds the frame square permanently, which is why braced gates stay fixed while re-tightened hinges alone often don't.
Basic cable-and-turnbuckle kits usually run about $10 to $20 at a hardware store, and they install with a drill in under half an hour. Wider or heavier gates may call for a sturdier kit or a gate wheel as well, which adds roughly another $15 to $30.
It depends on the material. A wood brace works in compression and runs from the bottom of the hinge side up to the top of the latch side. A cable kit works in tension and runs the opposite diagonal: top of the hinge side down to the bottom of the latch side.
Partly. Chain-link gates rack at the frame corners and respond to a turnbuckle cable on the same tension diagonal. Vinyl gates usually sag because the internal metal reinforcement has shifted or the hinges have pulled from the post — check the hinge mounting first, and use the reinforcement kits made for vinyl rather than wood-frame fixes.
There's no hard cutoff, but gates wider than about five feet, or built from heavy stock like double 2x6 rails, put a lot of leverage on two hinges. A spring-loaded gate wheel under the latch side is cheap insurance once you're in that territory.